United States Department of Agriculture

Agricultural Marketing Service

Federal Grain Inspection Service

Criteria & Specifications May 1, 2015

Distribution: Industry Originating Office: Technology and Science Division

COVER PAGE

Design Criteria for Unified Grain Moisture Algorithim (UGMA)

and Official System Compatibility

Contents

COVER PAGE �������������������������������������������������������������������������������������������������������������������������1

0. BASIC CRITERIA ����������������������������������������������������������������������������������������������������������������

1. UGMA COMPATIBILITY CRITERIA �������������������������������������������������������������������������������������

2. OFFICIAL SYSTEM COMPATIBILITY CRITERIA FOR UGMA MOISTURE METERS��������

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employer.
Design Criteria for Unified Grain Moisture Algorithim (UGMA)

and Official System Compatibility

Effective May 1, 2015

Page 2

0. BASIC CRITERIA

0.1 As a prerequisite for consideration, the instrument must be National Type Evaluatio

Program (NTEP)-certified as complying with all design criteria and performance 

requirements of the National Conference on Weights and Measures’ (NCWM) 

current Moisture Meter Code 5.56 (a) using the evaluation processes for moisture

meters specified in NCWM Publication 14.

0.2 The model number must clearly identify a UGMA-Compatible version of an NTEPcertified moisture meter if the original NTEP-certified version was not subject to

all standardization processes or hardware or software modifications needed to 

achieve UGMA-Compatibility. The manufacturer must ensure that the UGMAcertified version is also certified under NTEP prior to Official use

0.3 The temperature ranges for which the instrument may be used for official 

inspection will be no wider than those for which it is currently NTEP-certified.

0.4 If other conditions (such as, but not limited to, leveling) that were passed under

NTEP testing must be maintained more stringently to achieve the tolerances in 

this document, then the manufacturer is responsible to provide suitable means* 

to ensure proper operating conditions (such as a bubble level with appropriate 

sensitivity, for instance)

0.5 The proposed model must have been included in the NTEP Phase II Calibratio

Accuracy Study for at least one harvest season to allow FGIS to assess 

conformance to some of the criteria listed below.

0.6 The manufacturer is responsible to ensure that the instruments submitted for th

Phase II Calibration Accuracy Study (or those purchased by FGIS to serve as 

“standard” units for the model) are aligned and maintained to represent the model 

as “standard” units as defined within the criteria below.

0.7 Any operational deficiencies* or recurrent failure modes* identified by FGIS in the 

course of its testing of the model (but not otherwise specifically covered by the 

following list of Criteria) must also be resolved to FGIS’ satisfaction prior to the 

delivery of UGMA-Compatible instruments and to maintain FGIS approval for 

Official use.

0.8 For any hardware, software, or manufacturing process whose description is 

required to be submitted to demonstrate UGMA-Compatibility, the manufacturer 

shall not change such hardware, software, or manufacturing process without 

disclosing* such changes and detailed description thereof to FGIS for full review. 

Failure to do so may result in revocation of UGMACompatible status for the model

0.9 These criteria may be modified at the discretion of FGIS to reflect the current statu

 of an Official moisture system based on the UGMA. This could include additional 

requirements that were not previously envisioned but that are met by those 

instruments that have been previously certified as UGMA-Compatible.
Design Criteria for Unified Grain Moisture Algorithim (UGMA)

and Official System Compatibility

Effective May 1, 2015

Page 3

1. UGMA COMPATIBILITY CRITERIA 

1.1. The moisture meter design must be based on measurements of complex reflection 

coefficient or complex impedance of a parallel-plate transmission line type test 

cell at a precisely known and controlled frequency (+/- 0.05 MHz) within the range 

of 148.5 to 150.5 MHz. The manufacturer must provide a block diagram* of the 

measurement circuitry to illustrate what is actually being measured. The error 

analyses required (for Criteria 2.2, 2.5, etc.) that are affected by the measureme

frequency shall include assessment of the effects of measurement frequency error

1.2. The parallel-plate transmission line test cell must have (metrologically significant) 

dimensions* that are based on the “master” test cell design that FGIS uses for 

calibration development. (Detailed drawings of the master test cell are available 

from FGIS upon request, PDF_dwgs_14May08.zip.) The manufacturer must 

provide documentation* to demonstrate that variations in test cell dimensions are 

controlled sufficiently to have negligible effects (see Sensitivity Analyses section 

of UGMA Recipe Book) on dielectric constant measurements OR that the test cell 

model for each individual instrument is sufficiently corrected to cancel the effects of 

dimensional variations

1.3. A detailed microwave-type test cell model* (based on ABCD matrices, signal flow 

graphs, or equivalent) must be used to compute dielectric constant from complex 

reflection coefficient or complex impedance measured at the manufacturer-defined 

frequency. (This does not preclude the instrument actually using a lookup table to

implement the routine conversion to dielectric constant.) The manufacturer must

provide the test cell model*, including a description of the mathematics used, and 

test data* as needed to permit FGIS to verify its sufficiency. The expected level of 

detail is similar to that provided by FGIS in the following publication: DIELECTRIC 

REFERENCE MATERIALS FOR MATHEMATICALLY MODELING AND 

STANDARDIZING GRAIN MOISTURE METERS, D.B. Funk and Z. Gillay, Tr

ASABE, Vol. 53(1), 2010. (Reprint available upon request.) The dimensions* a

other parameters* used in the test cell model must be specified and the means* 

of arriving at those values must be described in sufficient detail for FGIS staff to 

assess their adequacy

1.4. The test cell must be loaded through a circular funnel opening that is designed to 

minimize the operator dependency on the orientation of kernels in the test 

cell. Grain types with elongated kernels are most sensitive to this problem and 

will be used by FGIS to assess the suitability of the sample loading design. 

Minimizing the funnel opening diameter (while avoiding bridging with moist coarse 

grains) tends to result in the least operator-dependence. The manufacturer

must supply a description* of experiments and results* performed to verify the 

operatorindependence of the loading method

1.5. The design* must ensure that sufficient grain is placed in the loading hopper to 

ensure overfilling of the test cell so that a constant struck-off volume is achieved. 

The manufacturer must provide documentation* to show how this is accomplished.
Design Criteria for Unified Grain Moisture Algorithim (UGMA)

and Official System Compatibility

Effective May 1, 2015

Page 4

1.6. The moisture meter must automatically strike off the filled test cell to provide a 

constant measured volume of grain. The manufacturer must provide the value of

the nominal volume* of the test cell and process* used in production to ensure that 

the volume is controlled (or measured and corrected) on production units

1.7. The moisture meter must determine the mass of the grain in the struck-off test cel

to a resolution of 0.1 g or bette

1.8. The instrument must determine and display sample temperature with a resolution of 

0.1 °C or better (or 0.1 °F or better if Fahrenheit display is provide

1.9. The instrument must use the steps and mathematics shown in UGMA Steps 1-8

(UGMA Recipe Book pgs. 3-6) and the coefficients (which will be updated 

periodically by FGIS) listed in the tables in the UGMA Recipe Book—except as 

allowed by Paragraph 1.10, below. The data produced at each intermediate step 

must be accessible in a recorded data stream (at least in a special test mode or 

with special calibration coefficients) with sufficient digital precision to allow FGIS 

headquarters staff to confirm that the instrument is correctly applying the specified 

equations and coefficients and to troubleshoot instrument problems.

1.10. Any grain-group-specific correction factors required to account for minor differenc

in loading methods must be applied prior to producing density-corrected dielectric 

constants. The use of any such corrections* must be completely documented* and

technically justified to demonstrate to FGIS that the correction is not inappropriately 

compensating for errors within the dielectric constant measurement system. The 

stability of any such corrections across similar grains must be documented*. The

appropriateness of the loading corrections must be established based upon: 

1) confirmation of the fitness of the test cell model*, 2) re-prediction of NTEP

Phase-II data (and/or other data)* with the manufacturer’s final test cell 

parameters*, and 3) final calibration review* (jointly with manufacturer and FGIS) of 

NTEP Phase-II calibration data (and/or other data) including volume ratio or other 

justified loading corrections.

1.11. The sample-by-sample agreement expressed as Standard Deviation of Differenc

(SDD) of the instrument (single tests) with the FGIS “master” UGMA system must 

be no worse than the SDD for the agreement of the FGIS “master” with the FGIS 

Air Oven method (single tests on UGMA) and no greater than 2 times the SDD of 

differences between two instruments of the model (single tests), (but the tolerance 

shall be no less than 0.15%) for each of the “major” grain types listed in Table 1 

for grain less than or equal to 20.0% moisture. This assessment will be based on 

data from the FGIS Annual Calibration Study, which is conducted at 22 +/- 2°C. 

FGIS will evaluate conformance to this requirement based on FGIS’ re-prediction 

of data* using final manufacturer-supplied test cell model parameters* and loading 

corrections*. Outliers shall be removed before computing the SDD values. Th

method for arbitrating decisions for identifying outliers will be the Grubb’s Test 

(approximately 3 standard deviations)
Design Criteria for Unified Grain Moisture Algorithim (UGMA)

and Official System Compatibility

Effective May 1, 2015

Page 5

1.12. The magnitude of the average bias (below 20% moisture) between the instrument 

model (average of two tests on each of two standard instruments) and the FGIS 

“master” UGMA system shall not exceed 0.10% moisture (+ 90% CI) for any 

“major” grain group (Table 1). This assessment* will be based on data from the 

FGIS Annual Calibration Study, which is conducted at 22 +/-2°C. FGIS will evaluate 

conformance to this requirement based on FGIS’ re-prediction of data using final 

manufacturer-supplied test cell model parameters* and loading corrections*

Outliers will be removed as described in 1.11.

2. OFFICIAL SYSTEM COMPATIBILITY CRITERIA FOR UGMA MOISTURE METERS

2.1. The FGIS Regulations (§ 801.6 Tolerances for moisture meters) state the bas

operational tolerances for “headquarters standard meters” and “other meters” 

as follows: (1) Headquarters standard meters. By direct comparison using midrange Hard Red Winter wheat, ±0.05% mean deviation from the average of the 

Headquarters standard moisture meters. (2) All other than Headquarters standard 

meters. By sample exchange using mid-range Hard Red Winter wheat, ±0.15% 

mean deviation from the mean value obtained by standard meters. Therefore, the

subsystems comprising standard instruments maintained at FGIS Headquarters 

must be capable of being “fine tuned” (but not metrologically different in any 

way from production instruments) to meet considerably tighter tolerances than 

normal production instruments. Production instruments must be standardized at

the factory (or repair center) to provide at least 90% confidence in meeting the 

sample exchange tolerances with Hard Red Winter wheat. Instruments failing 

the tolerance must be repaired at no charge (if under warranty) and demonstrate 

compliance with the tolerance prior to use in Official service (or being returned to 

Official service). The manufacturer shall submit documentation* to demonstrate 

the capability to achieve the 90% confidence in meeting the tolerance for individual 

instruments when tested with independent samples that were not used in the 

standardization/normalization production process.

2.2. The manufacturer must demonstrate and document* that the accuracy (0.67 tim

NCWM field verification meter-to-meter tolerances (+/-0.5% M x 0.67 = +/-0.335% M)

or better with respect to the FGIS “master” UGMA system (average of three tests)) 

for all grain types and moisture levels up to 22% moisture can be adequately 

assured by routine field testing of Official meters with medium moisture Hard Red 

Winter wheat (HRWW) (plus additional field-applicable tests that the manufacturer 

and FGIS may prescribe). Such additional tests may include a scale accuracy test

(see (2.3)) and/or a temperature accuracy test (see (2.4)). The goal of this Criterion 

is to confirm that a check test performed with HRWW is a viable way of verifying 

the instrument’s performance (or conformance to the model pattern) on every grain 

that might be tested. The manufacturer must document* how the instrument’s 

design and standardization processes* achieve this—assuming that the “standard” 

instruments for the model are closely aligned with the FGIS “master” UGMA

system. Again, this is not about absolute accuracy but rather about agreement

among all of a manufacturer’s production units—and how a practical set of in-field 

performance tests by Official inspectors can verify that agreement.
Design Criteria for Unified Grain Moisture Algorithim (UGMA)

and Official System Compatibility

Effective May 1, 2015

Page 6

2.3. It must be possible for the operator to capture the grain contained in the struck-of

test cell for subsequent external mass determination (with a precision grain 

scale)—for purposes of periodic performance testing of official moisture meters. 

The value of the measured mass of the grain in the test cell (resolution of 0.1

g or better) must be readily accessible to the operator without using auxiliary 

equipment. The tolerance for mass accuracy for new or newly repaired instruments 

(in comparison with precision grain scales) shall be +/- 0.3 grams, average 

difference for five tests. For routine field verification tests the tolerance shall be +/- 

0.5 grams, average difference for five tests. The accuracy tolerances apply over 

the range of cell weights corresponding to grain with test weights of 25 to 70 lb/bu.

2.4. The instrument must provide a suitable test mode and display of temperature to 

permit operator assessment of temperature measurement accuracy by comparison 

to a precision reference thermometer. The accuracy tolerance (average of three

tests) for Headquarters Standard Meters is +/- (0.2 °C + (0.05 x |T – 22 °C|)). For 

other Official instruments, the tolerance (average of three tests) is +/- (0.5 °C + 

(0.05 x |T – 22 °C|)). If the temperature readout is in Fahrenheit, the tolerances will 

be scaled accordingly. The manufacturer must provide documentation* to show 

how Headquarters Standard Meters will be adjusted to meet the tighter tolerances.

2.5. The manufacturer must describe in detail the processes* used to ensure tha

production instruments (and repaired instruments) are standardized (with respect 

to manufacturer’s production standard instruments) to provide agreement in 

density-corrected dielectric constant within +/-1% of reading (but not less than 

+/-0.027) (average of less than or equal to 5 repeat tests) for grain or artificial 

sample materials over the range of density-corrected dielectric constants from 2.2

to 8.0 with loss tangents of 0.03 to 0.2. (The ranges of dielectric constant and loss 

tangent for grains are shown in Figures 8-10 of the UGMA Recipe Book, and the 

moisture prediction errors associated with this 1% of reading tolerance are shown 

in Figure 12 of the UGMA Recipe Book.) Note that the tolerances for dielectric

constant measurements will need to be considerably tighter for Headquarters 

Standard Meters to meet the 0.05% matching on HRWW, and that the 1% 

tolerance is insufficient to ensure passing the field verification test (+/- 0.15% 

moisture for mid-moisture Hard Red Winter wheat, for which density-corrected 

dielectric constant is approximately 3.0), since it would exceed the moisture 

tolerance. (0.01 x 3 = 0.03; 0.03 x 6 = 0.18% M). Therefore, the density-corrected 

dielectric constant measurement accuracy will need to be controlled more carefully 

in the critical range around 3.

2.6. The manufacturer shall provide means* for FGIS to create calibration transfer files 

that permit updating calibrations electronically in all Official moisture meters. 

Such transfer files must allow for coexistence of calibration files from other 

UGMA instrument manufacturers on the same physical device (such as a USB 

drive) so that the same physical device can be used for updating any official 

UGMA-compatible meter model. The means* (programs, etc.) to create and alte

calibration files must be protected by strong passwords or other security to prevent 

unauthorized persons from altering Official or NTEP moisture calibration files.
Design Criteria for Unified Grain Moisture Algorithim (UGMA)

and Official System Compatibility

Effective May 1, 2015

Page 7

2.7. The instrument shall provide means* for measurement results to be output in rea

time via a RS232 serial interface (or through USB to serial adaptor) in a prescribed 

tab-delimited format (UGMA Criteria—Attachment A). It must also be possible for

the measurement results to be stored internally in the instrument and subsequently 

downloaded through a USB port or other similar means. Such downloadable file 

shall conform to a defined format (Attachment A) for compatibility in calibration data 

processing. The manufacturer may provide a user-selectable option for outputting

data in the FGIS-specified format rather than making that the only available format.

* The indicated information shall be considered company-proprietary and not 

subject to release under Freedom of Information Act (FOIA) requests. The lack of 

specific designation (*) as company-proprietary in this document shall not affect 

the proprietary status of relevant company-proprietary information.